I have a 2004 Ford Expedition Eddie Bauer...a couple years ago the unit that controls the direction of the rear air flow (floor/roof) stripped its gears out...we fixed this problem by just pinning the door closed to where it only blows from the roof. On a trip the other day I noticed all we have in the rear is ice cold air (it won't go to heat). Is there another box back there that controls the blend door? Any help will be appreciated and part model numbers would be great. Thanks.